At the Royal Courts of Justice in London, lawyers for the actor Hugh Grant and his former girlfriend, the socialite Jemima Khan — once the subject of relentless tabloid attention — mentioned The News of the World and unspecified “other newspapers” while demanding police information on Glenn Mulcaire, the private investigator who was jailed in 2007 for hacking into the phones of royal staff members. It was the first suggestion that Mr. Mulcaire, who had an exclusive contract with The News of the World, might have sold his information to other publications. Those publications were not named in the court proceedings, but the judge referred to “one or more newspaper proprietors.”

The phone hacking scandal at The News of the World has escalated into a political firestorm because it has swept up not only the tabloid's parent company, the News Corporation, owned by Mr. Murdoch, but also exposed close and questionable ties among the press, Scotland Yard and Britain's political elite.

But in Parliament on Wednesday, Mr. Cameron said it would be naïve to think that phone hacking was limited to Murdoch-owned newspapers. He named members to a panel that will have broad power to force newspaper owners, reporters, politicians and the police to give evidence under oath at public hearings into the culture, practices and ethics of the press. It will be led by Lord Justice Brian Leveson, a prominent judge, and includes former journalists, a civil rights campaigner and a retired law enforcement official.

Mr. Cameron was not alone in declaring the need for a broader look at Fleet Street.

On Tuesday, a member of Parliament accused the CNN anchor Piers Morgan of phone hacking when he was the editor of The Daily Mirror. Mr. Morgan strenuously denied the accusations and demanded an apology. And last week, news reports showed that the actor Jude Law has brought a hacking lawsuit against The News of the World’s sister newspaper, The Sun.

Five former journalists at The News of The World's rival Sunday newspaper, The People, run by the Mirror group, said in interviews that they regularly witnessed hacking in that newsroom in the late 1990s to early 2000. “I don't think anyone quite realized the criminality of it,” said one former reporter at The People, who spoke on condition of anonymity. A former reporter for the Sunday Mirror, another News of the World rival, described the extensive use of private detectives to obtain personal information. A former senior News of the World editor, Neil Wallis, who has been arrested on unspecified accusations of phone hacking, left The People in 2003 to join the Murdoch tabloid.

Nick Fullagar, director of communications for Trinity Mirror, the parent company of The Daily Mirror and The People, said, “Trinity Mirror’s position is clear. Our journalists work within the criminal law and the PCC code of conduct,” referring to Britain's press regulatory body, the Press Complaints Commission. Within Mr. Murdoch's empire, the flagship daily tabloid The Sun has also been accused of hacking phones. The lawsuit by Mr. Law, filed last month, says that four articles published in 2005 and 2006 were based on intercepted voice mail.

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The suit does not make clear which articles Mr. Law believes came from phone hacking, and News International, the British subsidiary of the News Corporation, has vehemently denied the accusation. A review of The Sun’s Web site, cross-referenced against news archives, shows that five articles from that period that cite phone calls, no source or very vague sources for intimate information about Mr. Law are no longer available on the tabloid's Web site.

In an article on April 15, the satirical news magazine Private Eye, which has long pursued accusations of hacking across Fleet Street, linked nine other articles at The Sun between 1998 and 2001 with the phone hacking scandal. The articles, which did not cite sources for celebrity gossip and referred extensively to phone calls, also are not available on The Sun's Web site. “I print everything out now, just in case it disappears,” said Adam Macqueen, a journalist at Private Eye who tracks the accusations of hacking at The Sun.

Mr. Grant's lawsuit is similar to those filed between 2007 and 2009 that first delved into Mr. Mulcaire's notes to reveal the extent of wrongdoing at The News of the World and were the catalyst for the current headlines.

Mr. Grant has played an activist role since the scandal broke, secretly recording a former News of the World journalist talking about how widespread the practice was and then publishing the conversation in the British news magazine The New Statesman in April.

Mr. Grant told the BBC that he visited a pub owned by Paul McMullan, a former editor for The News of the World, with his own recording device. Mr. McMullan, he said, told him that “it wasn't just The News of the World, it was all the tabloids.”